This invention relates to optical communication systems and, more particularly, to an apparatus and method for creating high repetition pulse trains and/or optically transmitting data in optical data telecommunications systems and generating data-modulated optical pulse trains (e.g. optical words) for use in such systems.
In view of increasing optical communication network demands, significant efforts are being expended in the development of high repetition rate pulse optical clock sources or optical clocks. Such optical clocks are a critical component in current and future optical networks. One attractive methodology is repetition rate multiplication of a lower rate source to generate very high repetition rate pulse bursts and/or trains. This methodology may use a modified arrayed waveguide grating (AWG). The arrayed waveguide grating, frequently used in optical communication systems as channel multiplexers/demultiplexers, has seen limited prior use in time-domain applications.
Such a standard AWG device is depicted in FIG. 1. Particularly, FIG. 1 shows a schematic diagram of an exemplary standard AWG 20 generally fabricated from planar glass layers (e.g. films of silica glass) deposited on a silicon, or other suitable substrate and processed using microelectronic fabrication techniques inherited from the silicon VLSI (Very Large Scale Integration) industry. AWG 20 consists of one or more input guides (Input(s)) represented by single input guide 22. Input guide 22 is connected to input slab waveguide 24.
AWG 20 also includes waveguide array 26 consisting of a plurality of waveguides having a constant length difference between adjacent guides in the array. Moreover, AWG 20 further includes output slab waveguide 28, and a series of output guides (Outputs) 30. In operation, light from input guide 22 is transferred to one of the output guides 30 depending on its wavelength due to the spectrometer structure of waveguide array 26 and output slab waveguide 28 which function as a grating/lens combination.
In prior time-domain applications, an AWG has been used to spectrally slice supercontinuum sources in order to generate pulse trains on multiple output channels. Alternatively, using a mode-locked source laser with the AWG permits the generation of trains of tens of picosecond pulses at the repetition rate of the source laser. An AWG excited by a single lower repetition rate laser generating high repetition rate burst or short pulses, or in principle a continuous train, as multiple, spatially separated output wavelengths, has also been shown to be analogous to a direct space-to-time (DST) pulse shaper previously demonstrated in bulk optics.
A methodology has been demonstrated by the present inventors for modifying the conventional AWG structure as presented in FIG. 2, and incorporating a short pulse laser source to excite the AWG in order to generate very high repetition rate pulse bursts. This modification may be considered a “PulseAWG”. A key design constraint of the PulseAWG is that the delay increment between adjacent guides in the waveguide array must be greater than the pulse width of the input pulse. In this case, the pulses from each guide of the waveguide array are temporally separated (spatial domain) and a pulse burst is generated with a pulse-to-pulse spacing (time domain) equal to the waveguide array delay increment. This design constraint arrangement may be termed a one-guide, one pulse methodology.
FIG. 2 presents a schematic representation 40 of the one-guide, one pulse methodology utilizing an AWG 42. An optical pulse or signal 44 is provided at input guide 46 of an input slab waveguide 48. A spatial profile of waveguide excitation 50 is provided to a waveguide array 52 wherein individual optical pulses 44 are excited. Wavelengths are separated at the output slab 60, wherein all the phases from each guide in the array are aligned so that the waveguide array acts like a combined grating/lens. This is represented by the temporal profile 54. The output slab region is essentially like the propagation region behind a bulk lens (i.e. an input collimated beam focuses a focal length away from the lens). An output pulse train 56 is thus provided on output guide 58 of output waveguide slab 60.
A further modification of the conventional AWG structure permits arbitrary pulse sequence generation. These arrangements yield multiple spatially separated output channels with identical temporal intensity profiles but varying center wavelength similar to operation of a bulk optic based apparatus that is known as a direct space-to-time (DST) pulse shaper. The DSTAWG pulse shaper has significant potential to impact the optical communications industry by integrating and simplifying the data transmission portions of ultrafast optical word generator systems or subsystem, i.e. for combining output data words from fast electrical interfaces and serializing them for transfer over an ultrafast optical channel. This parallel electrical to serial optical data stream conversion operation is a key bottleneck in high speed photonic (optic) networks. Thus, there is an ongoing need for further improvements in optical data telecommunications, particularly with respect to parallel electrical to serial optical data stream conversion. The current embodiments of DSTAWGs, however, are not necessarily optimum configurations.
It is therefore desirable to have a more efficient manner of producing ultrafast optical pulses particularly, but not exclusively, for use in optical communication systems.
It is therefore also desirable to have a more efficient manner of producing ultrafast optical data and/or words particularly, but not necessarily, for use in optical communication systems.
It is therefore further desirable to have a method and/or apparatus for producing ultrafast optical pulses.
It is therefore even further desirable to have a method and/or apparatus for producing ultrafast optical data and/or words.
It is therefore still further desirable to have a method and/or apparatus for converting a parallel electrical binary data word into a serial optical binary data word particularly, but not exclusively, for use in optical communication systems.
It is therefore even further desirable to have a method and/or apparatus for direct space-to-time mapping between a spatial pattern and a resultant ultrafast optical waveform for use in high-bit-rate data telecommunications wherein the spatial pattern represents data and/or word.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and in the associated figures.